1. Technical Field of the Invention
The present invention is related to a steel prop for supporting moldboards, and more particularly to a steel prop which is able to bear axial bidirectional applied force.
2. Prior Art
FIG. 1 shows a conventional steel prop 10 for supporting mold board. The steel prop 10 includes: an outer tube 12; an adjustment seat 13 fixedly connected with top end of the outer tube; a retaining nut 15 screwed around the adjustment seat 13 for adjusting height of the prop; an inner tube 16 formed with several pin hole 17 at equal intervals, the inner tube 16 being nested in the outer tube 12 and the adjustment seat 13; and an insertion pin 18 transversely passed through a slot 14 of the adjustment seat 13 and inserted in any of the pin holes 17 of the inner tube 16. In use, the inner and outer tubes 16, 12 are adjusted to a desired length. Then, the insertion pin 18 is inserted through the slot 14 of the adjustment seat 13 into one of the pin holes 17 of the inner tube 16. Then, the retaining nut 15 is screwed as shown by phantom line of FIG. 2 to retain the insertion pin 18. Accordingly, the extending length of the inner and outer tubes 16, 12 can be adjusted for supporting moldboards.
The above steel prop 10 has many imperfections. For example, when adjusting the length, it is time-consuming and inconvenient to operate the prop 10. Moreover, the insertion pin 18 contacts with the periphery of the pin hole 17 only at a point with small contacting area. Therefore, a shear stress is likely to be applied to the prop and the strength of the prop is poor.
In order to solve the above problems, an improved steel prop 20 has been developed as shown in FIG. 3. Such prop 2 includes an outer tube 22, an inner tube 24, two engaging members 25 and a locking member 28. The top end of the outer tube is formed with a conic face 23. The body of the inner tube 24 is formed with a thread and nested in the outer tube 22. The inner circumference of each engaging member 25 is formed with transverse thread section 26. The two engaging members 25 are positioned on the conic face 23 of the outer tube 22 and connected by a pin member 27 on one side. The locking member 28 is disposed on the other side of the engaging members 25.
In use, as shown in FIG. 5, when the wedge locking bar 29 of the locking member 28 is positioned at an upper dead end, the two engaging members 25 are not mated with each other so that they do not mesh with the inner tube 24. At this time, the inner tube 24 is upward pulled out as shown in FIG. 6. After pulled to a certain length, a user can downward knock the locking bar 29 with a tool as shown in FIG. 7. Accordingly, the two engaging members 25 are mated with each other and the thread sections 26 thereof mesh with the thread of the inner tube 24 as shown in FIG. 8. Under such circumstance, the inner tube 24 is prevented from retracting into the outer tube 22. Accordingly, the prop can be used to support moldboards.
Such steel prop 20 can be more quickly adjusted in length so that the time for adjustment is saved. In addition, the thread sections 26 of the engaging members contact with the inner tube on a face so that the inner tube is firmly clamped to provide higher supporting strength.
However, it is found that the above steel prop 20 still has shortcomings. For example, the steel prop can only bear axial pressure, while failing to bear axial tension. In other words, in locked state, the inner tube of such steel prop is prevented from retracting into the outer tube. However, the inner tube is not prevented from moving out of the outer tube. Therefore, when subject to a pulling force and pulled outward, the inner tube will slide within the outer tube. Accordingly, the steel prop can be only used in an upright state to resist against axial pressure, while failing to bear axial pulling force. Therefore, such prop can be hardly used in an oblique state or a horizontal state to support moldboards. As a result, the application field of such prop is limited.
In addition, the conventional steel prop has more components which are exposed to outer side. For example, the insertion pin 18 and the movable handle 151 of the retaining nut 15 of FIG. 1 are exposed to outer side. Also, the locking bar 29 of FIG. 3 is exposed to outer side. These exposed components tend to injure workers due to collision. Moreover, when transferring or stacking the steel props, the exposed components tend to damage due to collision.
It is therefore a primary object of the present invention to provide a steel prop which is able to bear both axial pressure and pulling force. Therefore, the application field of the steel prop is widened.
It is a further object of the present invention to provide the above steel prop which is able to bear axial bidirectional applied force. In addition, the steel prop has no components projecting toward outer side so that the possibility of injury of workers and damage of the steel prop can be minimized.
The present invention can be best understood through the following description and accompanying drawings wherein: